1. Field of the Invention
The invention concerns itself with systems and methods for monitoring cardiac action of a patient physically distant from stationary facilities for measuring and analyzing cardiac data.
2. Description of the Prior Art
The value of portable cardiac monitoring devices which sense and transmit cardiac information to distant facilities for processing, display, and analysis has become increasingly recognized. In addition to the many advantages of existing nonportable monitoring devices having the capability of providing cardiac information to distant facilities, such as providing access to sophisticated research and treatment centers and permitting tests to be conducted in physicians' offices, it has been recognized that portable devices would have significant favorable aspects. Such systems may be activated at any time by the user when he senses symptoms of cardiac malfunction or may be operated routinely in accordance with a prescribed program. These functions may be carried out with minimum disruption of the routine of the patient.
There have, however, been many problems in implementing portable cardiac monitoring devices. The stationary monitoring systems are not adaptable to being made portable. These systems generally comprise a standard EKG device equipped with means for transmitting or storing cardiac information for transfer to a distant medical facility. These standard systems are predicated upon isolating the patient from his normal activities and environment. For example, the patient must be isolated from common 60 cycle electrical sources to avoid common mode disturbance of the recorded cardiac signals. The patient must be muscularly relaxed to avoid muscular artifacts in the reading and must be motionless to eliminate error due to static electrical charge. The patient's skin must be specially prepared, usually by abrasion of the epidermal layer, to obviate the problem of artifacts due to variations in skin resistance. Moreover, existing systems utilize a large number of patient contact electrodes interconnected to one another to obtain patterns of cardiac potential related to the conventional EKG data. The interconnections among the electrodes are in some cases through resistors and form a complex network along the patient's body. The expense and bulk of such complex systems have been a substantial problem.
A frequently seen portable system is one having a minimal number of leads to obviate somewhat the problems of unwieldiness and complexity of lead structure of the above-discussed devices. Such simple systems pay a substantial price, however, in diminution of information. Moreover, there has been no significant attack on the problems, which arise particularly frequently with ambulatory patients, of common mode vulnerability and instability of signal due to variations in skin resistance of the patient. Moreover, existing systems suffer from the drawback that the electrodes which they utilize are often affixed over muscle or other tissue and thus introduce muscular artifacts into the sensed potentials from the heart for the non-muscularly relaxed patient. Existing systems further tend to lack the versatility achieved by combining EKG or cardiac monitoring with monitoring of a pacemaker.
Therefore, there has been a recognized but unfulfilled need for a portable cardiac action monitoring system, having the capability of providing substantial cardiac information, as well as pacemaker information, which is not compromised in its ability to process cardiac signals by ambient electrical noise, by fluctuations in skin resistance of the patient or by muscular artifacts and is at the same time economical and sufficiently comfortable, convenient, compact, and lightweight to meet the physical and social needs of ambulatory patients utilizing the device. Monitoring systems which fulfill these requirements must also, if possible, provide transmittable signals for conventional communications systems (e.g. telephones) that can be used after demodulation for recordation by conventional means, such as an EKG recorder or tape recorder.